The Gem Tester with color estimator display for smooth, seamlessly testing of precious gems and diamonds. The SmartPro Gem-Eye I was specifically developed to distinguish between diamonds and other simulants, using the principle of thermal conductivity. The exceptional heat conductivity of diamonds is unlike any simulant. Therefore, diamonds are not easily replicable. The SmartPro Gem-Eye I consists of two linked thermometers; 1 that is heated electronically, while the other is cooled by the gem being tested. The difference in temperature creates an electrical output, which is then amplified and displayed on an analog dial. The color gem estimator display assists the user in distinguishing popular colored gems from each other.